local a = "致远电子"
assert((ulen(a) == 4))
assert((ulen((a + "abc")) == 7))
assert((usubstr(a) == "致远电子"))
assert((usubstr(a,0) == "致远电子"))
assert((usubstr(a,0,1) == "致"))
assert((usubstr(a,0,-1) == "致远电"))
assert((usubstr(a,-2,-1) == "电"))
assert((usubstr(a,-3) == "远电子"))
assert((usubstr(a,-3,ulen(a)) == "远电子"))
